The present invention is directed to a clutch mechanism that disengages the rotational drive to the drill bit assembly when a hole of the desired depth has been drilled.
It is frequently desirable when drilling holes, in castings for example, to drill a hole to a particular precise depth. Such applications are typical when drilling holes in cast engine blocks, or the like, that may have a fluid cavity that must not be penetrated or where a clamp is to be positioned at a certain depth from the surface. These castings have irregular surface features that make it difficult for the drill operator to know when the desired depth has been reached. Currently, in drilling these orifices, the CNC (computer numerically controlled) machine operator must stop the machine, make a calculation based on the configuration of the surface and manually adjust the depth, altering the computer program for each orifice drilled. Alternatively, a sensor may be used to determine the surface characteristics of the casting and alter the computer program to provide the desired drilled depth.
The present invention provides a clutch mechanism for limiting the depth of penetration by a drill, the clutch mechanism comprising an arbor having a first end insertable within a spindle of a machine tool and a second hollow end; a collet holder having a first end partially received within the hollow end of the arbor, a central portion having drive surfaces thereon, and a second end receiving and securing a drill bit therein, the arbor, the collet holder and the drill bit forming an inner assembly; clutchable drive means positioned between the arbor and the collet holder, means for mounting said locking ring on the second hollow end of the collet holder, the means for mounting permitting relative longitudinal movement therebetween; sensing means for determining when the drill bit has reached a desired maximum penetration depth; whereby, when the sensor means determines that the maximum depth of penetration has been reached by the drill bit, the clutchable drive between the arbor and the collet holder is disengaged to prevent further drilling.
In the preferred embodiment, the sensing means comprises a nose cone assembly including a nose cone surrounding a portion of the second end of the collet holder and at least a portion of the drill bit; means attaching the nose cone assembly to a ball locking ring such that the nose cone assembly and ball locking ring move longitudinally as an outer unit, the ball locking ring having a first inner diameter engaging a plurality of locking balls and holding them in a first position in contact with the drive surfaces of said collet holder and a second larger inner diameter maintaining the locking balls in said apertures but permitting the locking balls to move to a second position disengaged from the drive surfaces of the collet holder; whereby, when the distal end of the nose cone contacts a workpiece being drilled, forward movement of the outer unit is halted and relative longitudinal movement of the inner assembly over a short distance permits the locking balls to move from the first diameter of the ball locking ring to the second diameter disengaging rotational drive of the collet holder and drill bit, thereby limiting the depth of penetration of the drill bit.
The means for mounting the nose cone to the ball locking ring includes a coarse thread on two engaged members enabling the position of the nose cone relative to the drill bit to be readily adjusted to alter the depth at which the drive clutch is disengaged. A first spring biases the outer assembly to its forward most position when the nose cone is disengaged with the surface of the workpiece. A second spring also biases the collet holder and attached drill bit to their extended position such that the ball locking ring re-positions the locking balls in the drive races once again when the forward push on the assembly is relieved. A first slide bushing positioned within the hollow end of the arbor facilitates relative longitudinal movement between it and the collet holder. A second slide bushing mounted in a recess in an upper end of the locking ring facilitates relative longitudinal movement between it and the arbor so that the ball locking ring may collapse upon the arbor once the locking balls have moved to their second disengaged position.
A cap nut threadingly engages a lower portion of the adjusting ring, the cap nut capturing the nose cone assembly and securing it to a remaining portion of the outer unit. A bearing positioned between the clutch assembly and the remaining portion of the outer unit permits the balance of the outer unit to continue to freely rotate once a downward force on the nose cone against the workpiece brings the nose cone assembly to rest. A stop nut threadingly engaging the coarse thread on the exterior of the ball locking ring positioned against an upper surface of the adjusting ring prevents undesired movement thereof.
The nose cone assembly includes a connector ring having a first internal thread which engages a threaded portion of said nose cone, and a second internal thread which engages an external thread on an inner cap ring, the inner cap ring having an outwardly extending flange which is surrounded by an inwardly protruding flange on a lower portion of the adjusting ring.
Various other features, advantages and characteristics of the present invention will become apparent to one of ordinary skill in the art after a reading of the following specification.